Power MOSFET contact metallization

ABSTRACT

A structure includes a semiconductor device formed in a substrate; an insulator adjacent to the semiconductor device; an electrical contact electrically coupled to the semiconductor device, wherein the electrical contact includes tungsten; and an electrical connector coupled to the electrical contact, wherein the electrical connector includes aluminum. A surface of the insulator and a surface of the electrical contact form a substantially even surface.

RELATED U.S. APPLICATIONS

This application claims priority to the provisional patent application, Ser. No. 60/799,868, entitled “Power MOSFET Contact Metallization,” with filing date May 12, 2006, assigned to the assignee of the present application, and hereby incorporated by reference in its entirety. This application is a divisional of and claims priority to the copending U.S. patent application Ser. No. 11/799,889, entitled “Power MOSFET Contact Metallization,” with filing date May 2, 2007, and hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

Embodiments in accordance with the present invention generally pertain to semiconductor devices, in particular power metal oxide semiconductor field effect transistors (power MOSFETs).

BACKGROUND

Photolithography is commonly used to fabricate semiconductor devices. In photolithography, a pattern from a mask is transferred to a surface. Light is directed through the mask and focused on the surface. As features of semiconductor devices get smaller and smaller, better focus becomes more important.

SUMMARY

A method and/or system that facilitate the use of photolithography to fabricate semiconductor devices with small features would be advantageous. Embodiments in accordance with the present invention provide this and other advantages.

In one embodiment, a structure includes a semiconductor device formed in a substrate; an insulator adjacent to the semiconductor device; an electrical contact electrically coupled to the semiconductor device, wherein the electrical contact includes tungsten; and an electrical connector coupled to the electrical contact, wherein the electrical connector includes aluminum.

In one embodiment, a surface of the insulator and a surface of the electrical contact form a substantially even surface. The substantially even surface improves focus during photolithography, so that smaller sized features can be formed on the surface.

These and other objects and advantages of the present invention will be recognized by one skilled in the art after having read the following detailed description, which are illustrated in the various drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention:

FIG. 1 is a sectional view showing selected layers of a structure according to one embodiment of the present invention.

FIG. 2 is a flowchart of a process that is used in the fabrication of the structure of FIG. 1 according to one embodiment of the present invention.

FIGS. 3, 4 and 5 are sectional views showing selected stages in the fabrication of the structure of FIG. 1 according to an embodiment of the present invention.

FIG. 6 is a top-down view of a portion of the structure of FIG. 1 according to one embodiment of the present invention.

FIG. 7 is a sectional view showing selected layers of a structure according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one skilled in the art that the present invention may be practiced without these specific details or with equivalents thereof. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.

Some portions of the detailed descriptions that follow are presented in terms of procedures, logic blocks, processing, and other symbolic representations of operations for fabricating semiconductor devices. These descriptions and representations are the means used by those skilled in the art of semiconductor device fabrication to most effectively convey the substance of their work to others skilled in the art. In the present application, a procedure, logic block, process, or the like, is conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present application, discussions utilizing terms such as “forming,” “performing,” “producing,” “depositing,” “etching” or the like, refer to actions and processes (e.g., process 200 of FIG. 2) of semiconductor device fabrication.

It is understood that the figures are not drawn to scale, and only portions of the structures depicted, as well as the various layers that form those structures, are shown. For simplicity of discussion and illustration, the process is described for one or two transistors, although in actuality more than one or two transistors may be formed.

Furthermore, it is appreciated that other fabrication processes and steps may be performed along with the processes and steps discussed herein; that is, there may be a number of process steps before, in between and/or after the steps shown and described herein. Importantly, embodiments of the present invention can be implemented in conjunction with these other (perhaps conventional) processes and steps without significantly perturbing them. Generally speaking, the various embodiments of the present invention can replace portions of a conventional process without significantly affecting peripheral processes and steps.

FIG. 1 is a sectional view showing selected layers of a structure 10 according to one embodiment of the present invention. As mentioned above, structure 10 may include other devices, elements and layers beyond those illustrated and described.

In the example of FIG. 1, two devices 14 and 16 are formed within substrate 12. In one embodiment, substrate 12 is a silicon substrate.

Devices 14 and 16 are, in general, complementary metal oxide semiconductor (CMOS) devices. More specifically, in one embodiment, devices 14 and/or 16 are power metal oxide semiconductor field effect transistors (power MOSFETs). The details of devices 14 and 16 are not illustrated or described. Devices such as power MOSFETs are known in the art, and embodiments in accordance with the present invention can accommodate different varieties of power MOSFETs. In one embodiment, devices 14 and/or 16 are trench power MOSFETs.

In the example of FIG. 1, a contact 22 is positioned between device 14 and device 16, so that these devices can make electrical contact with each other or with other devices. Connector 24 in turn is in electrical contact with contact 22. In one embodiment, contact 22 is composed of tungsten, and connector 24 is composed of aluminum, although the present invention is not so limited.

In the present embodiment, insulators 18 and 20 are adjacent to devices 14 and 16, respectively. Insulators 18 and 20 may be composed of silicon dioxide or borophosphosilicate glass (BPSG), although the present invention is not so limited. The insulators 18 and 20 serve to isolate the devices 14 and 16, although either or both of the devices 14 and 16 are electrically coupled to contact 22. In other words, there is a specific conductive path from device 14 and/or from device 16 to contact 22.

With structure 10 oriented as in FIG. 1, the upper surface of contact 22 is essentially level with the pre-metal dielectric (PMD) surface 26. The upper surfaces of contact 22 and insulators 18 and 20 form a substantially flat surface. As will be seen from the discussion below, the substantially flat surface formed by contact 22 and insulators 18 and 20 facilitates the fabrication of smaller sized features, in particular smaller sized elements such as contact 22 and connector 24.

FIG. 2 is a flowchart 200 of a process that is used in the fabrication of the structure 10 of FIG. 1 according to one embodiment of the present invention. Although specific steps are disclosed in FIG. 2, such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in FIG. 2. FIG. 2 is discussed in conjunction with FIGS. 3, 4 and 5, which are sectional views showing selected stages in the fabrication of the structure 10 of FIG. 1 according to an embodiment of the present invention.

In block 201 of FIG. 2, with reference also to FIG. 3, a structure that includes device 14 is fabricated, or a structure so fabricated is received. In one embodiment, a first barrier layer 30 is deposited over the insulators 18 and 20 and over the area of substrate 12 between insulators 18 and 20. The area between insulators 18 and 20 is the contact area in which contact 22 of FIG. 1 will be formed. In one embodiment, the first barrier layer 30 is composed of titanium-nitride (TiN).

In block 202 of FIG. 2, with reference also to FIG. 3, a first metallized layer 32 is deposited over the first barrier layer 30. The first metallized layer 32 is deposited over the insulators 18 and 20 and in the contact area between insulators 18 and 20. In one embodiment, the first metallized layer 32 includes tungsten. Another material, such as copper, may instead be used. In one embodiment, the first metallized layer 32 is deposited using chemical vapor deposition (CVD).

In block 203 of FIG. 2, with reference also to FIG. 4, the first metallized layer 32 is, in one embodiment, etched (planar etched) to the PMD surface 26 of FIG. 1. In other words, the first metallized layer 32 is etched back to the first barrier layer 30, so that the upper surface of the remaining portion of the first metallized layer 32 is essentially level with the upper surfaces of insulators 18 and 20. Thus, a substantially level surface 40 (which may correspond to the PMD surface 26) is formed across the insulators 18 and 20 and across the contact area between insulators 18 and 20.

The surface 40 so formed is level enough to improve focus during photolithography. That is, if a surface is too uneven, then parts of the surface may be in focus while other parts of the surface may be out of focus. However, in accordance with embodiments of the present invention, surface 40 is level enough to allow the parts of the surface that are of interest to remain in focus during photolithography. By improving focus across the surface, smaller sized features (e.g., connector 24 of FIG. 1) can be formed on the surface 40.

Furthermore, the width of the contact area (indicated as dimension D in FIG. 4) can be reduced. One advantage of reducing the contact area is that the density of devices (e.g., devices 14 and 16 of FIG. 1) can be increased. As the width D is reduced in size, materials such as aluminum may no longer be adequate for filling in the contact area, in order to form a proper contact. In accordance with embodiments of the present invention, CVD of the first metallized layer 32—in one embodiment, CVD of tungsten—is used to adequately fill smaller contact areas, forming a proper contact 22. In one embodiment, dimension D is in the range of approximately 0.35-0.50 microns.

In block 204 of FIG. 2, with reference also to FIG. 5, in one embodiment, a second barrier layer 33 is deposited over the surface 40. In one embodiment, second barrier layer 33 is composed of titanium.

In block 205 of FIG. 2, with reference also to FIG. 5, a second metallized layer 34 is deposited over the second barrier layer 33. In one embodiment, the second metallized layer 34 includes aluminum.

In block 206 of FIG. 2, a mask (not shown) is used according to a photolithographic process to pattern the second metallized layer 34. The second metallized layer 34 is etched to form connector 24 of FIG. 1.

FIG. 6 is a top-down view of the structure 10 of FIG. 1 according to one embodiment of the present invention. In the example of FIG. 6, connector 24 traverses a number of individual contacts 22 after the etch process of block 206 (FIG. 2). Although individual contacts 22 are illustrated in FIG. 6, embodiments in accordance with the present invention are not so limited. For example, embodiments in accordance with the present invention can also utilize continuous contacts (that is, as if the individual contacts 22 were joined to form a single contact).

FIG. 7 is a sectional view showing selected layers of a structure 70 according to another embodiment of the present invention. In contrast to the contact 22 of structure 10 of FIG. 1, which may be referred to as a planar contact, the contact 71 of FIG. 7 extends into the substrate 12. Contact 71 may be referred to as a trench contact. With structure 70 oriented as in FIG. 7, contact 71 extends below the upper surface 72 of substrate 12.

Contacts 71 and connector 24 of structure 70 can be formed using process 200 of FIG. 2. In block 201 of FIG. 2, with reference also to FIG. 3, a structure that includes device 14 and a trench adjacent to device 14 is fabricated, or a structure so fabricated is received. The remaining steps of process 200 are then performed as described above.

In summary, embodiments in accordance with the present invention facilitate the use of photolithography to fabricate semiconductor devices with smaller features. Smaller contacts can be formed by depositing a material such as tungsten into smaller contact areas. The resulting structure is etched to form a substantially even surface. The relative evenness of the surface improves focus and allows reduced size features to be formed on the surface.

Embodiments of the present invention are thus described. While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the below claims. 

What is claimed is:
 1. A method of fabricating a structure, said method comprising: depositing a barrier layer, wherein said barrier layer is deposited over and in contact with all surfaces of an insulator except for a second surface of said insulator that is in contact with a first surface of a substrate having a semiconductor device formed therein, wherein said barrier layer is also deposited over and in contact with said substrate in a contact area between said insulator and an adjacent insulator; depositing a first metallized layer over said barrier layer; and etching said first metallized layer to form an electrical contact in said contact area, wherein a substantially even surface is formed by combining a surface of said barrier layer and a surface of said electrical contact, wherein said barrier layer is between and in contact with said substrate and said electrical contact, and said semiconductor device is adjacent to and underneath said insulator and entirely isolated physically from said electrical contact and from said barrier layer by said insulator, said semiconductor device electrically coupled to said electrical contact.
 2. The method of claim 1 wherein said first metallized layer comprises tungsten.
 3. The method of claim 1 wherein said first metallized layer is deposited using chemical vapor deposition.
 4. The method of claim 1 wherein said semiconductor device comprises a power metal oxide semiconductor field effect transistor.
 5. The method of claim 1 further comprising: depositing a second metallized layer subsequent to said etching; and etching said second metallized layer to form an electrical connector coupled to said electrical contact.
 6. The method of claim 5 wherein said second metallized layer comprises aluminum. 